Hello I am using a modified anet a6 with ramps 1.4 octopi etc i added a relay to my heatbed and tried the extruder as well but the extruder relay once hitting temp was constantly open/ closing many times a second. Is the extruder voltage from ramps a pulse rather than steady the bed w is great closed when heating open when not but the extruder is crazy. Any tips?
The heater cardridge is PID controlled which translates to a pulse signal on the RAMPS output, using a relais is not recommended for this. Normal cardridges are 40W which draws about 3.3A @ 12V, why would you not let the RAMPS take care of this? The FETs on the board are well able to handle this current draw. Using a relais on the heatbed make more sense though.
huntley
November 4, 2017, 11:25pm
3
You should not use a relay for controlling the hotend (extruder) temperature. It doesn’t require very much current, so the MOSFET transistors on your RAMPS 1.4 board will be more than large enough to control it.
The way an Arduino/RAMPS controls the temperature for the hotend is by rapidly turning it on and off. The percentage of the duty cycle when it is on determines how hard it is trying to heat up the hotend. So, yes, it rapidly pulses the current to the hotend.
I use a solid state relay on my hot bed. No problems for 2 years
Mirth
November 5, 2017, 1:22am
5
Ahhhhh yeah, you should probably read up on how this stuff actually works… your bed is probably set to bang-bang but your hot end will be PWM. there is absolutely no need to use a relay, I don’t know where you got that impression. If you wanted to you could use a solid state relay which would eliminate the noise and mechanical wear buuuuuut they’re actually made up of one or more transistors so there’s no point.
your motherboard should have a MOSFET transistor for each heated unit (bed and any nozzles). They’re there for a reason. Just attach straight to those.
Mirth
November 5, 2017, 1:25am
6
Yes and no. Solid state relays are pretty much just transistors with the occasional diode or two. I’m running a 24V 350W heated bed through the original mosfet that came on my RAMPS1.4. It’s perfectly capable of handling the power, it just needed a decent heatsink on it. Transistors are incredibly powerful things!
There is of you want to use a 24 volt bed with the ramps 1. 4 board
av8r1
November 5, 2017, 4:56am
8
Don’t use a relay on the nozzle heater; the controller uses pulse width modulation to fine tune the temperature of the nozzle, and the pulses are much faster than a relay can keep up with. The MOSFET transistor on the RAMPS board is perfectly capable of handling the current required of the nozzle.
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Hello, for this application You have to use a solid state relay.
Mirth
November 5, 2017, 9:07am
11
Not true, have you ever looked at what’s inside an SSR? One or more transistors and possibly some diodes and capacitors. I run my 24V 350W bed through the original MOSFET on my RAMPS1.4. It’s more than capable, you just need to make one or two slight modifications to the board and put a decently large heatsink on the MOSFET for proper thermal dissipation and then it works perfectly well.
That’s besides the point anyway as the question was about the hot end.
You do it your way and I’ll do it my way Cheers
This is logical because the temperature will never stay at the desired setpoint, it wil lower and rise because of cooling. For this the relay will try to open/close many times per second. This is normal. The only thing is tough, a normal relay is not made for these kind of applications and wil break really fast. Therefore I advise you to start using some kind of mosfet.
Either switch out for a solid state relay or change the heating to work on a bang bang principle. That’s what I did for my large bed that draws around 2.5kw on start up and needed a 200amp power solenoid to control reliably.
Just use a solide state relay. Rapid switching is normal for low mass heating. Lookup PID.
Mirth
November 5, 2017, 3:43pm
16
Dude, how big is your bed???
It’s a PID loop for the extruded, thus the relay is getting voltages between open and closed state and cycling. I recommend not using a relay and looking to something else.
